The present invention is directed in general toward filtering devices and, more particularly, toward a combination integrate and dump filter and level detector.
Integrate and dump filters comprise filtering devices provided for integrating a voltage input over a specified time interval and, thereafter, providing the result of the integration as the filter output. These devices are generally employed for determining the cumulative polarity of the input signal over the integration time interval. As an example, integrate and dump filters have been employed to detect a data signal which has been phase shift modulated onto a carrier signal. U.S. Pat. No. 4,641,325 to Hughes. As another example, integrate and dump filters have been used to determine the synchronism of a baud signal with the input signal.
Prior art integrate and dump filters have proven bulky and expensive as excess circuitry has been provided to insure that the filter can integrate during the dump interval. Such insurance is generally necessary to provide a result which is accurate over the entire integration period. Hence, prior art integrate and dump filters have generally provided two capacitors and apparatus for switching each into the filter circuit such that one capacitor can be integrating while the other is dumping. Further, prior art integrate and dump filters have generally required additional elements for detecting and amplifying the integrated output such that an input signal having a slightly positive cumulative polarity over the baud period will provide a fully positive filter output and, conversely, an input signal having a slightly negative cumulative polarity over the baud period will provide a fully negative filter output.
It would be advantageous, therefore, to provide a combination integrate and dump filter and level detector which eliminates the need for excess capacitors and amplifiers and therefore greatly reduces production costs. Further, it would be advantageous to provide such an integrate and dump filter which also provides high immunity to coherent interference which is known to accompany phase shift modulated transmissions.